Plasma etch reactor and method for emerging films

ABSTRACT

A plasma etch reactor  20  includes a reactor chamber  22  with a grounded upper electrode  24,  a lower electrode 28 which is attached to a high frequency power supply  30  and a low frequency power supply  32,  and a peripheral electrode  26  which is located between the upper and lower electrode, and which is allowed to have a floating potential. Rare earth magnets  46, 47  are used to establish the magnetic field which confines the plasma developed within the reactor chamber  22.  The plasma etch reactor  20  is capable of etching emerging films used with high density semiconductor devices.

This application is a divisional of Ser. No. 08/675,093, filed Jul. 3,1996, now U.S. Pat. No.6,048,435.

CROSS-REFERENCE

The following U.S. patent applications, all owned by Tegal Corporation,are cross-referenced and hereby incorporated by reference:

1. Title: PLASMA ETCH REACTOR AND METHOD

Inventors: Stephen P. DeOrnellas, Leslie G. Jerde Alfred Cofer, RobertC. Vail, Kurt A. Olson

Ser. No.: 08/675,559

Filed: Jul. 3, 1996

2. Title: PLASMA ETCH REACTOR HAVING A PLURALITY OF MAGNETS

Inventors: Stephen P. DeOrnellas, Leslie G. Jerde Alfred Cofer, RobertC. Vail, Kurt A. Olson

Ser. No.: 09/152,238

Filed: Sep. 11, 1998

3. Title: PLASMA ETCH REACTOR AND METHOD FOR EMERGING FILMS

Inventors: Stephen P. DeOrnellas, Alferd Cofer, Robert C. Vail

Ser. No.: 08/675,093

Filed: Jul. 3, 1996

4. Title: PLASMA ETCH REACTOR AND METHOD FOR EMERGING FILMS

Inventors: Stephen P. DeOrnellas, Alferd Cofer, Robert C. Vail

Ser. No.: Unknown

Filed: Aug. 27, 1999

Docket No.: TEGL 1009-DIV-1 SRM

5. Title: IMPROVED METHOD AND APPARATUS FOR ETCHING A SEMICONDUCTORWAFER WITH FEATURES HAVING VERTICAL SIDEWALLS

Inventors: Stephen P. DeOrnellas, Alferd Cofer, Robert C. Vail

Ser. No.: 08/742,861

Filed: Nov. 1, 1996

FIELD OF THE INVENTION

The present invention relates to an improved plasma etch reactorapparatus and method.

BACKGROUND OF THE INVENTION

A new set of emerging films are being beneficially employed in thedevelopment of high density semiconductor chips such as for example highdensity DRAM. These materials provide for higher capacity devices byallowing a reduction in the size of the individual features on thememory device. Accordingly, enhanced selectivity and profile control arerequired.

In the past, ion mills, which are a slow physical process, have beenused to establish desired profiles on semiconductor wafers. Such ionmills have disadvantages in that the profile formed on the semiconductorwafer is sensitive to the angle of the ion mill beam and thus, the ionmill beam has to be accurately positioned to obtain the requiredprofile. When profiles are obtained, however, large veils or ribssticking up from the edges of the desired profiles have beenexperienced. Accordingly, ion mills are not well suited to emergingfilms.

Plasma etch processes for use in emerging films are faster, however suchprocesses can in some cases provide unacceptable feature profiles.Accordingly, there is a need to provide an etching process which quicklyand accurately process the emerging films that are used in the latestsemiconductor products.

SUMMARY OF THE INVENTION

The present invention is directed toward a plasma etch reactor which cansuccessfully process emerging films used in high density semiconductordevices.

The present invention provides for a plasma etch reactor which has areactor chamber and an upper electrode which is grounded, a lowerelectrode which is connected to high frequency power supply, and a lowfrequency power supply, and a peripheral or ring electrode which ispositioned between the upper and lower electrodes. The potential forsaid peripheral or ring electrode is allowed to float. Alternatively,the ring electrode can be grounded. Such a reactor can successfullyprocess the newest emerging films used in high density semiconductorproducts.

It is a further object of the present invention to provide the reactorchamber with magnets in order to produce a high magnetic field, and thusa sufficiently dense plasma in order to successfully etch the newestemerging films.

It is a further object of the present invention to have the density andetch characteristics of the plasma controlled by one or more of thepower sources.

Other objects and advantages of the invention will be obtained from areview of the descriptions, claims and figures.

BRIEF DESCRIPTION OF THE FIGS.

FIG. 1 is a side cross-sectional view of an embodiment of the plasmaetch reactor of the invention.

FIG. 2 is a view similar to FIG. 1 with the addition of an enhancedprocess gas inlet nozzle.

FIGS. 3a and 3 b depict end and side cross-sectional views of apreferred embodiment of a nozzle of the invention.

FIGS. 4a, 4 b, 4 c, and 4 d depict isometric, side cross-sectional,enlarged partial side cross-sectional, and end views of anotherpreferred embodiment of a nozzle of the invention.

FIGS. 5a, 5 b, and 5 c depict side cross-sectional, enlarged partialcross-sectional, and end views of yet another preferred embodiment of anozzle of the invention.

FIGS. 6a, 6 b, and 6 c depict side cross-sectional, enlarged partialcross-sectional, and end views of still a further embodiment of a nozzleof the invention.

FIG. 7 depicts a perspective view of the arrangement of the magnetsassociated with a peripheral electrode of an embodiment of theinvention.

FIG. 8 depicts a perspective view of the arrangement of the magnetsassociated with the upper electrode of an embodiment of the inventionshown in association with the magnets of FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the figures and in particular to FIG. 1, a sidecrosssectional view of an embodiment of the plasma etch reactor 20 ofthe invention is depicted. This reactor 20 enhances and improves uponthe reactor depicted and described in U.S. Pat. No. 4,464,223, whichpatent is incorporated herein by reference.

Reactor 20 includes a reactor chamber 22 which is bounded by a groundedupward electrode 24, a side peripheral electrode 26, and a bottomelectrode 28. The side peripheral electrode 26 is grounded or has afloating potential and in operation can be charged up by the plasma. Ina preferred embodiment, the bottom electrode 28 is connected to a powersupply 30 which provides power to the bottom electrode 26 preferably at13.56 MHz (or multiples thereof) at a power level of preferably 900watts and at a voltage of preferably 1,200 volts. The high frequencypower supply can operate from 10 watts up to 2000 watts in a preferredembodiment. It is to be understood that this is a high frequency powersupply (preferably in the radio frequency range) and that the frequencypreferably can range from 2 MHz to 40 MHz and upwards to about 900 MHz.The power can also preferably be supplied in the range of 100 watts to3,000 watts with a voltage of between 200 volts to 5,000 volts.

A second power supply 32 is additionally connected to the bottomelectrode 28. The second power supply 32 is preferably operated at 450KHz with the power being preferably supplied at 100 watts, and at avoltage of 300 volts. This is the low frequency power supply. It is tobe understood that this power supply (preferably in the radio frequencyrange) can be operated in the range of about 100 KHz to about 950 KHz(preferably 1 MHz or less) with a power range of 10 watts to 2,000watts, and a voltage range of 10 volts to 5,000 volts. Also connected tothe bottom electrode 28 is a DC power supply 34. The high-frequencypower supply controls ion flux, while low-frequency power supplyindependently controls ion energy.

It is the control of the power supplies and principally the highfrequency power supply which advantageously controls the density of etchplasma in order to provide superior etch characteristics. Further, it isthe design of reactor 20 which provides the enhanced plasma densityrange from which the optimal plasma density can be selected by thecontrol of the power supply.

Associated with the grounded upward electrode 24 is a central nozzle 36which directs a jet of process gas into the reactor chamber 22 directedat the semiconductor wafer 48. As will be discussed below in greaterdetail, the jets of process gas from the nozzle 36 are able toeffectively reach the surface of the semiconductor wafer 48 and providea fresh, uniform distribution of process gas over the entire surface ofthe semiconductor wafer 48.

Immediately above the grounded upper electrode 24 and the nozzle 36 isan exhaust stack 38, which is used to exhaust spent gas species from thereactor chamber 22. It is to be understood that a pump (not shown) issecured to the exhaust stack 38 in order to evacuate the gas speciesfrom the reactor chamber 22.

As can be seen in FIG. 1, immediately below the upper electrode 24 andnozzle 36 is a protruding, peripheral baffle 40. Baffle 40 is comprisedof insulating material, and as will be discussed below, protrudes intothe exhaust path 42 between the nozzle 36 and the housing 44 of theplasma etch reactor 20. Protruding baffle 40 ensures that there is agood mixture of the various gas species from the nozzle 36 and the solidsource 50 in the reactor chamber 22.

Immediately below the protruding baffle 40 and in this embodimentincorporated into the side peripheral electrode 26 is a magnet orplurality of magnets 46. Also preferably incorporated in upper electrode24 is a magnet or plurality of magnets 47. As will be discussed below,either one or both of these magnets 46 and 47 define a magneticconfinement chamber about and coincident with the reactor chamber 22.This magnetic confinement chamber ensure that the charged ion species inthe reactor chamber do not leak therefrom, and that the charge ionspecies are concentrated about the semiconductor wafer 48. This magneticconfinement chamber inhibits the charged ion species from collecting onthe walls of the reactor chamber 22.

Covering the side peripheral electrode 26 and the magnets 46 is a sideperipheral solid source 50. Such a solid source is not required in thepreferred embodiment as there is no power provided to the ring electrode26. If, however, in addition to the above power source preferably, ahigh frequency power source were provided to the solid source 50, thenthis solid source 50 would provide for an innovative source of a gaseousspecies which can be sputtered through the bombardment of, for example,radio frequency excited ions which knock or erode atoms of the gasspecies from the solid source 50 into the reaction chamber 22. Theerosion of gaseous species from the surface of the solid source can beaffected by the pulsing of power supplies. As a further advantage, asportions of the surfaces of the solid source erode, no particles can beformed on the eroding surfaces by the combination of gaseous species.Thus, contamination from such particles formed on eroding portions ofthe solid surfaces are eliminated. Variations of the solid source 50 arediscussed hereinbelow.

Immediately below the solid source 50 is the wafer chuck 52 whichpositions the semiconductor wafer 48 relative to the reactor chamber 22.Wafer clamp 53 holds the wafer 48 on the wafer chuck 52. In thisembodiment, the wafer chuck 52 as well as the bottom electrode 28 can bemoved vertically downward in order to insert and remove the wafer 48.

In this embodiment, if desired, the side peripheral electrode 26 and themagnets 46 can be cooled using a cooling water manifold 54. It isfurther to be understood that the solid source 50 can be heated ifdesired using a hot water manifold 56. Other methods of heating thesolid source 50, and particularly the front exposed surface thereof,include resistive and inductive heating, and radiant heat provided bylamps and other sources of photons.

The protruding baffle 40 as well as the configuration of the magnets andthe process gas jets from the nozzle, and the gas species eroded fromthe solid source (if a power supply is connected to the peripheral ringelectrode 26), provide for a high density plasma adjacent to the surfaceof the semiconductor wafer. This configuration greatly increases therange of densities that can be achieved within the reactor chamber 22.

The above range of operation is not possible with prior devices. It isto be understood that one or more of the above features can be used toenlarge the plasma density range and thus improve the etch process andfall within the spirit and scope of the invention.

An alternative embodiment of the reactor 20 is shown in FIG. 2. Similarcomponents are numbered with similar numbers as discussed hereinabove.In FIG. 2, the nozzle 36 has been modified in order to improve theuniformity of the mixture of the gaseous species in reactor chamber 22.As can be seen in FIG. 2, the nozzle 36 includes a manifold 70 which canchannel the process gases in a number of directions. From manifold 70there are horizontal ports 72, 74 which direct jets of the process gaseshorizontally and parallel to the upper electrode 24. Port 76 directsjets of the gas vertically downward directly onto the wafer 48. Ports 78and 80 channel jets of the process gases in a direction skewed to thehorizontal, and principally toward the periphery of the wafer 48 inorder to assure a uniform distribution of process gases and/or a goodmixture of the gas species. In this embodiment, it is also thecombination of the ports of the manifold 70 and the protruding baffle 40which ensures that a good mixture of (1) the gas species sputtered oreroded from the solid source 50 (if a source of power is connected toperipheral ring electrode 26), and (2) the process gases from the portsof the nozzle 36, are presented to the surface of the semiconductorwafer 48.

Etching in prior art devices is usually performed in the 300 to 500millitorr range, which range is one to two orders of magnitude higherthan the low pressures contemplated by the reactor of the presentinvention. For etching of submicron features required bystate-of-the-art semiconductor devices, low pressure operations aredesirable. However, at low pressures, it is more difficult to maintain ahigh density plasma.

For the embodiments of FIGS. 1 and 2, the present invention contemplatesa magnetic field which contains the plasma at a low pressure (3-5millitorrs), with a high plasma density (10¹¹cm³ at the wafer), and withlow ion energy (less than 15 to 300 electron volts). Generally, lowpressure operation would be at about 150 millitorr or about 100millitorr or less and preferably about 20 millitorr or about 10millitorr or less. For submicron (sub 0.5 microns) devices, the plasmasource must operate at a low pressure with a high density of activatedgases at the wafer and a low ion energy in order to deliver superioretching results. A low pressure plasma improves the overall quality ofthe etch by minimizing the undercutting of the wafer features as well asthe effect of microloading (etching concentrated features more rapidlythan less concentrated features), both of which can adversely affectoverall yield. Low pressure, however, requires a high density plasma atthe wafer to increase the number of plasma particles reacting with afilm on the semiconductor wafer being etched in order to maintain a fastetch rate. A fast etch rate is one factor leading to a higher averagethroughput. Further, low ion energy leads to improved etch selectivityand minimizes wafer damage. Both of which improve overall yield. It iscontemplated that the present embodiment can operate at about 150millitorr or less.

The reactor 20 of the present invention can be used to etch a variety ofdifferent substrates or films which require different etch chemistry orrecipe. Principally, the embodiments of the invention are used to etchthe new emerging films. Generally, this chemistry includes two or moreof the following gases: halogen gases, halogen containing gases, noblegases, and diatomic gases.

Variations of the above features describe above will now be explained ingreater detail.

Solid Source

Again, it is to be remembered that the solid source only comes intooperation if a power supply is connected to the peripheral ringelectrode 26. However, if a power supply, preferably a high frequencypower supply such as power supply 30, is connected to peripheralelectrode 26 in an alternative embodiment, then the following applies.

It has been determined that the gaseous species eroded or sputtered fromthe solid source 50 or the lack of species eroded or sputtered therefromcan have a profound effect on the success of the etching process carriedout in the plasma etch reactor 20. By way of example only, the solidsource 50 can be comprised of a dielectric material such as for examplesilicon dioxide (SiO₂) or quartz which upon bombardment by radiofrequency excited ions provide gaseous ions of silicon and oxygen fromthe solid source into the reaction chamber. Another type of dielectricsolid source can include a ceramic such as alumina (AL₂O₃). This ceramichas a low sputtering or erosion rate when impacted by excited gaseousions and is useful for situations where no additional contribution froma solid source is required or desired. Particularly, with respect toalumina, with a power supply under approximately 600 volts peak to peak,little or no sputtering is observed. Over that threshold, there issputtering from an alumina solid source.

Generally, the solid source can be comprised of a semiconductormaterial, a dielectric material, or a conductor. In fact, the solidsource could be embodied in the materials which comprise the electrode,and those materials can be eroded to provide appropriate gas species forthe plasma in the reactor chamber. Appropriate dielectric materials alsoinclude silicon nitride (Si₃N₄), in addition to other metal oxidesbesides alumina (Al₂O₃). Semiconductor materials can include siliconcarbide (SiC).

The surface temperature of the solid source 50 is preferably above 80°C. in order to provide for adequate sputtering. At this temperature andwith the appropriate energized ions eroding the surface of these solidsource, the solid source does not become a cold sink for the formationof particles, as discussed herein, from gaseous species, which particlescan break away and contaminate the reaction chamber 22.

As discussed above, the rate of erosion or sputtering of the gaseousspecies from the solid source 50 can be controlled by plurality the highfrequency power supply (not shown but similar to supply 30). Byincreasing the power supply (not shown but similar to supply 30), higherenergy ions can be used to bombard the solid source 50 in order toincrease the rate of erosion of gaseous species from the solid sourcefor purposes of the etching process. By way of example, should a solidsource of silicon dioxide be used, increased bombardment would enhanceanisotropic etching as the gaseous species sputter from the silicondioxide would passivate vertical surfaces on the semiconductor wafer sothat such surface would not be undercut by the gaseous etchant species.

Gaseous Source

In addition to the above benefits described with respect to the gaseousspecies eroded from the solid source, such benefits can also be acquiredby introducing in the process gases, gases which have the effect derivedfrom the gaseous species eroded from the surface of the solid source. Byway of example only, a gaseous form of tetraethoxysilane (TEOS) can beintroduced with the process gas. TEOS is a source of silicon and oxygenfor the etching process. TEOS in the process chamber provides the samegaseous species as does a solid source of silicon dioxide (SiO₂) withthe advantages to the etching process described herein. Also it is to benoted that a combination of both solid source and a gaseous source ofsuch species would be within the spirit and scope of the invention.

Nozzles

FIGS. 3a, 3 b, 4 a, 4 b, 4 c, 4 d, 5 a, 5 b, 5 c, 6 a, 6 b, and 6 cdepict alternative preferred embodiments of nozzle arrangements whichcan be used with the above invention. Conventional nozzle arrangementsare generally configured in a “shower head” configuration with as manyas 200 ports from which process gases to be ejected. The intent of suchan arrangement was to ensure that there was a uniform distribution ofthe process gases in the chamber, and in particular, at the surface ofthe semiconductor wafer that was being processed. Prior art devices havebeen found to create a layer of stagnate, used gases which have alreadyreacted with the wafer surface and thus dilute the uniformity of newprocess gases directed toward the surface. The present inventionimproves upon such prior art nozzles. The present invention includesnozzles which generate discrete collimated jets of process gases whichmerged together adjacent the wafer surface to create a uniformdistribution at the surface of the wafer. The velocity of the gases andthe volume in the jets assure that fresh process gas reaches the surfaceof the semiconductor wafer. Thus, fresh process gases are uniformallydistributed at the surface of the semiconductor wafer. These process gasjets stir up the gases at the surface of the wafer making a uniformdistribution of process gas and gaseous species eroded from the surfaceof the solid source.

FIGS. 3a and 3 b depict a one-port nozzle 90 with the port identified as92. The nozzle is preferably comprised of alumina. With thisarrangement, a single jet of gas is projected toward the semiconductorwafer.

FIGS. 4a, 4 b, 4 c, and 4 d depict another preferred embodiment of anozzle 94 of the invention which is also comprised of alumina. In thisembodiment, the nozzle 94 includes twelve ports which define jets ofprocess gas that are directed toward the semiconductor wafer.Preferably, the jets are directed at an angle which is skew to verticaland the centerline of each jet is directed toward the peripheral edge ofthe wafer. This arrangement is again beneficial in ensuring that thereis a uniform distribution of new process gases at the surface of thewafer. As can be seen in FIG. 4d, the ports are distributed around theperiphery of the face of the nozzle.

FIGS. 5a, 5 b, and 5 c depict a further embodiment of a nozzle 98 of theinvention. In this arrangement, the ports 99 are depicted in a starformation with some of the ports being provided on the periphery of theface (FIG. 5c) of the nozzle 98 while other of the ports are centrallylocated with one port on the centerline of the nozzle. As with the gasesfrom the nozzle of FIG. 4a, the jets of the nozzle of FIG. 5a are angledwith respect to the vertical and thus are directed both at the body ofthe semiconductor wafer and at the edge of the semiconductor wafer inorder to provide a uniform distribution of process gas.

FIGS. 6a, 6 b, and 6 c depict yet another preferred embodiment of thenozzle 100 of the invention. In this embodiment, ports 102 are directedessentially normal to a vertical line between the nozzle and thesemiconductor wafer. In this embodiment, the nozzles are directed towardthe solid source on the side wall in order to ensure greater mixing ofthe gas species from the solid source and the process gas.

Emerging Films

It is noted that the above reactors are particularly useful in etching anew class of emerging films used in new chip designs. By way of exampleonly, these reactor configurations are useful in the etching of platinum(Pt), currently being used in the development of high density DRAMdevices. Further, these reactors are useful in etching of lead zirconiumtitanate (PZT), currently being used in the development of non-volatile,ferro-electric random access memory (FRAM) devices. Additionally, thisreactor is useful in the etching of Iridium (Ir). Yet, another emergingfilm which can be successfully etched using this apparatus and method iscomprised of bismuth strontium tantalate (Y-1). While these new filmscontribute to improved, circuit performance, their unique propertiesmake them particularly difficult to etch, and therefore, require themore advanced etch process techniques of the present invention. Otheremerging films that can be processed with the preferred embodimentinclude barium strontium titanate (BST), iridium oxide (IrO₂), ruthenium(Ru), and ruthenium oxide (RuO₄).

It is to be understood that these new emerging films have significantadvantages in the latest semiconductor devices. By way of example,dielectrics used in older semiconductor devices have a dielectricconstant of between 2 and 4. With PZT the dielectric constant is 1400.Thus, the new memory devices made with such films can be significantlysmaller (with smaller features) and have more memory capability.Further, such films can be used to fashion capacitors for DRAMs andnon-volatile memories which can thus replace devices such as EPROMs,SRAMs, etc.

It has been observed that the dual frequencies on the bottom electrode28 are beneficial in the successful etching of the emerging films forthe latest semiconductor products. This arrangement allows for etchingdevice features which appropriate anisotropic side wall profiles inorder to accommodate the reduced critical dimensions, which are in thesubmicron range of about 0.25 microns and less.

Magnetic Confinement

The above identified magnets 46, 47 provide a magnetic confinementaround reactor chamber 22 which ensures that a high density plasma canbe formed at low pressure. It is to be remembered that the plasma iscreated through a collision of gas atoms and electrons, generating ionsto create a high density plasma at low pressure. The present inventionachieves this by increasing the total path length of the electronstraveling through the plasma while minimizing ion loss to the reactorwall. The electrons traveling toward the plasma are reflected by themagnetic field back into the plasma thus increasing the path length ofthe electrons.

With the present invention, the magnets can either be electromagnets orpermanent magnets and be within the spirit and scope of the invention.These magnets, surrounding the etched chamber, create a static magneticfield container. The magnetic field effect exists only near the reactorwalls, is virtually non-existent at the wafer, creating an inherentlyuniform plasma. The magnets provide the function of protecting theelectrodes as with a stronger magnetic confinement, there is lesserosion on the electrodes. A weaker confinement provides for moreerosion of the electrode and the solid source.

The magnetic confinement caused by the magnets 46, 47, thus is designedto concentrate the plasma and can have the effect of protecting theprocess chamber parts, including the electrodes from the corrosiveplasma. As a result, there are considerable cost savings, as the costfor replacing the electrodes is reduced.

FIGS. 7 and 8 depict an arrangement of the magnet 46, 47, in associationwith the side electrode 26 and the upper electrode 24 respectively. Ascan be seen in FIG. 7 there are a plurality of slots 60 found relativeto the electrode 26. In a preferred embodiment, every other of the slots60 are filled with the magnet 46. These magnets located behind the solidsource 50 affect the rate of erosion of gas species from the solidsource. As indicated above, without the magnets, it is possible that toomany gaseous species can be eroded from the solid surface and thusaffect the etch process.

It is to be noted that these magnets are pole face magnets. The northand south poles are on the faces 62 and the opposing faces 64 of themagnets. The magnets are arranged alternatively so that first a northpole face of one magnet 46 and then a south pole face of a second magnet46 are directed toward the center of the chamber. This is repeated aboutthe outer periphery of the electrode 26.

FIG. 8 depicts the arrangement of the magnets 47 associated with theupper electrode 24. Again, these magnets are pole faced magnets, withthe north and south poles projecting from the side faces of the magnets.For the configuration of FIG. 8, the magnets alternate with the northand then the south poles facing towards the chamber.

For this embodiment, the magnetic confinement chamber of the presentinvention preferably uses powerful rare earth magnets in order toprovide an optimal confinement for the plasma in the reactor chamber.

Rare earth magnets minimize the effect of electrons and gaseous ionsleaking from the reactor chamber 22. This aids in increasing the densityof the plasma and thus the efficiency of the etching process. In apreferred embodiment, the rare earth magnets are comprised of samariumcobalt. Preferably, these magnets have a magnetic strength at thesurface of between 2,000 GAUSS and 2,200 GAUSS. Generally, however,these rare earth magnets can have a strength at the surface of between1,500 and 2,500 Gauss.

In a particular embodiment, the peripheral electrode 26 retains sucheighteen (FIGS. 7, 8) rare earth magnets placed side by side on theperiphery of the reactor 20. The grounded upper electrode 24 hasassociate therewith twenty-four (FIG. 8) such rare earth magnets in apreferred embodiment. These magnets are arranged to provide a symmetricmagnetic field in the reactor chamber 22. With respect to the rare earthmagnets 47 associated with the grounded upper electrode 24, thesemagnets are provided in a spoke arrangement around a central point. Thearrangement is comprised of magnets which extend from the central pointtoward the periphery and magnets which extend from the periphery to aposition short of the central point. As indicated above, such rare earthmagnets give maximum repulsion of charged particles and electrons at thewalls of the reactor chamber 22. With such a configuration, there is notmuch sputtering or erosion of gaseous species from the solid source(especially when the peripheral electrode 26 is grounded or floating)and thus, silicon dioxide (SiO₂) can be used as the solid source ratherthan the more expensive alumina (AL₂O₃).

Reactor Chamber

The reactor chamber in the present invention has been specificallydesigned, as discussed above and below, in order to enhance theuniformity of the plasma. With respect to the physical characteristicsof the reactor chamber 22, as noted above, both the placement of thebaffle 40 and the nozzle 36, 70 contribute to the uniformity of theprocess gases in the reactor chamber 22. The baffle 40 ensures that thegas species eroded from the surface of the solid source 50 (particularlyif a power supply is connected to the peripheral electrode 26) are notimmediately drawn up by the pump through the exhaust shaft 38, but areallowed to mix with the gases in the reactor chamber adjacent to thesemiconductor wafer 48. Additionally, the nozzle 38 having ports whichchannel jets of gases vertically, horizontally, and at skewed anglesensure that any gas species from the solid source are thoroughly mixedwith the process gases from the nozzle and that this uniform mixture isprovided to the semiconductor wafer 48.

The height of the reactor chamber from the nozzle to the surface of thesemiconductor wafer can be optimized. Prior art devices have a height of5¼″. It has been found that with the above described height and also thenozzle arrangements can be optimized in order to have the gas jets fromthe nozzle provide a uniform distribution of process gas at the surfaceof the semiconductor wafer. Thus, also for varying reactor heights,nozzle pattern compared to chamber pressure can be optimized for theetch process including the etch process using a solid source. Thisheight is irrespective of the diameter of the reactor chamber, althoughin a preferred embodiment, the reactor chamber is approximately 14½″ indiameter. By way of example only, for preferred operation at two tothree millitorr of pressure in the reactor chamber 22, the height of thereactor chamber would be preferably about 4″. For a height of less than4″, the jets would still be collimated and thus not uniformally spreadat the surface of the wafer. For a height greater than 4″, the jetscould merge together above the surface of the semiconductor wafer so asnot to provide a uniform distribution of process gases at the surface ofthe wafer.

Optimally, for a given nozzle configuration, it has been found that theproduct of the height of the reactor chamber 22 with the pressure in thechamber, should be constant in order to provide for optimal performance.Thus, as indicated above, optimal performance can be achieved with aheight of 4″ and a pressure of two to three millitorr.

The range of values for pressure and height include a height range of{fraction (1/10)} of an inch corresponding to 100 millitorr to a heightof 10″ corresponding to one millitorr for optimal performance. That isto say that as the pressure increases in the reactor chamber, that theheight of the reactor chamber can be less and that as the pressuredecreases, the height would increase in order to provide for optimalmixing of (1) the gases eroded from the solid source, (2) injectedprocess gases, and (3) reaction products from the wafer surface.

The effect of the above invention is to (1) increase the selectivity(i.e., for example protect the oxide substrate), (2) enhance the profilecontrol of the etch process, and (3) enhance the line width control(i.e., protecting the photoresist from the etching process so that thecorrect line width is transferred from the photoresist to the wafer).

INDUSTRIAL APPLICABILITY

From the above, it can be seen that the present invention afford anapparatus and method which can successfully etch emerging films used tofabricate high density semiconductor devices such as high densitysemiconductor memories.

Other features, aspects and objects of the invention can be obtainedfrom a review of the figures and the claims.

It is to be understood that other embodiments of the invention can bedeveloped and fall within the spirit and scope of the invention andclaims.

We claim:
 1. A plasma etch reactor comprising: a reactor chamber; afirst electrode; a second electrode; a first power source connected tosaid second electrode which generates power at a first frequency; asecond power source connected to said second electrode which generatespower at a second frequency; said second electrode is associated with achuck which is adapted for holding a wafer to be processed; said firstpower source generates power at a low frequency; said second powersource generates power at a high frequency; and a third electrodeconnected to a third power source which generates power at a lowfrequency.
 2. The reactor of claim 1 including: a plasma confinementdevice that is adapted to contain a plasma in the reactor.
 3. Thereactor of claim 2 including: said reactor chamber including an upperwall, a lower wall, and a peripheral side wall which is located inbetween the upper wall and the lower wall; said second electrode locatedadjacent to said lower wall and said confinement device located adjacentto said peripheral side wall.
 4. The reactor of claim 3 including: saidconfinement device located additionally adjacent to said top wall. 5.The reactor of claim 3 wherein: said confinement device includes aplurality of magnets which are substantial parallel and are locatedabout said peripheral side wall.
 6. The reactor of claim 3 wherein: saidconfinement device includes a plurality of magnets; and said magnets arerare earth magnets.
 7. The reactor of claim 3 wherein: said confinementdevice includes a plurality of magnets; said reactor chamber has acenter; and said magnets are pole face magnets with north pole and southpole faces, and said magnets are arranged alternately so that first anorth pole face of one magnet and then a south pole face of a secondmagnet are directed toward the center of the reactor chamber.
 8. Thereactor of claim 3 wherein: said confinement device includes a pluralityof magnets associated with said peripheral side wall; said firstelectrode is associated with said upper wall; and said confinementdevice includes another plurality of magnets that are associated withsaid first electrode.
 9. The reactor of claim 8 wherein: said upper wallhas a center; and said another plurality of magnets associated with saidupper wall are positioned along radii extending outwardly from thecenter of said upper wall.
 10. The plasma etch reactor of claim 2including: a magnetic confinement associated with said reactor chamber.11. The plasma etch reactor of claim 10 wherein: said magneticconfinement is comprised of rare earth magnets.
 12. The plasma etchreactor of claim 11 wherein: said rare earth magnets are samarium cobaltmagnets.
 13. The plasma etch reactor of claim 2 including: saidconfinement device having one or more magnets positioned about thereactor chamber; and each said magnet having a strength of about 1,500Gauss to about 2,500 Gauss at the surface.
 14. The plasma etch reactorof claim 13 wherein: a magnetic field established by said rare earthmagnets is symmetrical.
 15. The plasma etch reactor of claim 1 wherein:said reactor is capable of etching high conductivity materials.
 16. Theplasma etch reactor of claim 1 wherein: said reactor is capable ofetching high conductivity materials to submicron dimensions.
 17. Theplasma etch reactor of claim 1 wherein: said reactor is capable ofetching films of at least one of lead zirconium titanate (PZT), platinum(Pt), iridium (Ir), bismuth strontium tantalate (Y-1), barium strontiumtitanate (BST), iridium oxide (IrO₂), ruthenium (Ru), and rutheniumoxide (RuO₄) to submicron dimensions.
 18. The plasma etch reactor ofclaim 1 wherein: said reactor is capable of etching wafers forferro-electric random access memories (FRAMs).
 19. The plasma etchreactor of claim 1 wherein: said first power source generates power at ahigh frequency of about 2 MHz to about 950 MHz; and said second powersource generates power at a low frequency of about 10 KHz to about 1MHz.
 20. The plasma etch reactor of claim 1 wherein: said first powersource generates about 10 watts up to about 2,000 watts; and said secondpower source generates about 100 watts up to about 3000 watts.
 21. Theplasma etch reactor of claim 1 wherein: said reactor chamber is capableof operating at about 150 millitorr or less and preferably 50 millitorror less.
 22. The reactor of claim 1 wherein: said first electrode is oneof electrically floating or at ground.
 23. The plasma etch reactor ofclaim 1 wherein: said first power source generates power at about 1 MHzor less; and said second power source generates power at about 2 MHz orgreater.
 24. The plasma etch reactor of claim 1 wherein: said secondpower source generates power at about 13.56 MHz; and said first powersource generates power at about 450 KHz.
 25. An enhanced plasma etchreactor comprising: a reactor chamber; a first electrode; a secondelectrode spaced from said first electrode; a first power sourceconnected to said second electrode which generates power at a firstfrequency; a second power source connected to said second electrodewhich generates power at a second frequency; a plasma confinement devicethat is adapted to contain a plasma in the reactor; said secondelectrode is associated with a chuck which is adapted for holding awafer to be processed; and a solid source of at least one gaseousspecies.
 26. The reactor of claim 25 including: a third power sourceconnected to said first electrode.
 27. The reactor of claim 26 wherein:said first, second, and third power sources are AC power source sources;and a DC power source connected to said second electrode.
 28. Thereactor of claim 27 wherein: said first, second, and third power sourcesare AC power source sources; and a DC power source connected to saidsecond electrode.
 29. The reactor of claim 26 including: a third powersupply connected to said first electrode.
 30. The reactor of claim 29wherein: said first, second, and third power sources are AC power sourcesources; and a DC power source connected to said second electrode. 31.An enhanced plasma etch reactor comprising: a reactor chamber; a firstelectrode; a second electrode spaced from said first electrode; a firstpower source connected to said second electrode which generates power ata first frequency; a second power source connected to said secondelectrode which generates power at a second frequency; a plasmaconfinement device that is adapted to contain a plasma in the reactor;said second electrode is associated with a chuck which is adapted forholding a wafer to be processed; and a solid source of at least onegaseous species covering said first electrode.
 32. The reactor of claim31 including: a third power source connected to said first electrode.33. The reactor of claim 32 wherein: said first, second, and third powersources are AC power source sources; and a DC power source connected tosaid second electrode.
 34. An enhanced plasma etch reactor comprising: areactor chamber; a first electrode; a second electrode; a first AC Dowersource connected to said second electrode which generates power at afirst frequency; a second AC power source connected to said secondelectrode which generates power at a second frequency; and a third DCpower source connected to said second electrode.
 35. The plasma etchreactor of claim 34 wherein: said first power source generates power atabout 1 MHz or less; and said second power source generates power atabout 2 MHz or greater.
 36. The plasma etch reactor of claim 34 wherein:said second power source generates power at about 13.56 MHz; and saidfirst power source generates power at about 450 KHz.
 37. The plasma etchreactor of claim 34 including: a magnetic confinement associated withsaid reactor chamber.
 38. The reactor of claim 34 including: a solidsource of at least one gaseous species.
 39. A plasma etch reactorcomprising: a reactor chamber: a first electrode; a second electrode;said first electrode is one of electrically floating or at ground; afirst power source connected to said second electrode which generatespower at a low frequency; a second power source connected to said secondelectrode which generates power at a high frequency; a plasmaconfinement device that is adapted to contain a plasma in the reactor;said second electrode is associated with a chuck which is adapted forholding a wafer to be processed; a third electrode connected to a thirdDower source which generates power at a low frequency; said first powersource, said second power source, and said third power source being ACpower sources; and a fourth power source connected to said secondelectrode, said fourth power source being a DC power source.
 40. Theplasma etch reactor of claim 39 wherein: said first power sourcegenerates power at about 1 MHz or less; and said second power sourcegenerates power at about 2 MHz or greater.
 41. The plasma etch reactorof claim 39 wherein: said second power source generates power at about13.56 MHz; and said first power source generates power at about 450 KHz.42. An enhanced plasma etch reactor comprising: a reactor chamber; afirst electrode; a second electrode spaced from said first electrode; afirst power source connected to said second electrode which generatespower at a first frequency; a second power source connected to saidsecond electrode which generates power at a second frequency; saidsecond electrode is associated with a chuck which is adapted for holdinga wafer to be processed; and a solid source of at least one gaseousspecies.
 43. The reactor of claim 42: including a plasma confinementdevice that is adapted to contain a plasma in the reactor.
 44. Anenhanced plasma etch reactor comprising: a reactor chamber; a firstelectrode; a second electrode spaced from said first electrode; a firstpower source connected to said second electrode which generates power ata first frequency; a second power source connected to said secondelectrode which generates power at a second frequency; said secondelectrode is associated with a chuck which is adapted for holding awafer to be processed; and a solid source of at least one gaseousspecies covering said first electrode.
 45. The reactor of claim 44:including a plasma confinement device that is adapted to contain aplasma in the reactor.
 46. The reactor of claim 44 including; a thirdpower source connected to said first electrode.
 47. An enhanced plasmaetch reactor comprising: a reactor chamber; a first electrode; a secondelectrode spaced from said first electrode; a first power sourceconnected to said second electrode which generates power at a firstfrequency; a second power source connected to said second electrodewhich generates power at a second frequency; said second electrode isassociated with a chuck which is adapted for holding a wafer to beprocessed; said reactor chamber including an upper wall, a lower wall,and a peripheral side wall which is located in between the upper walland the lower wall; said second electrode located adjacent to said lowerwall; a third electrode located adjacent to said peripheral side wall;said first power source generates power at a low frequency; said secondpower source generates power at a high frequency; and a third powersource connected to said third electrode located adjacent to saidperipheral wall, said third power source generates power at a lowfrequency.
 48. The reactor of claim 47: including a plasma confinementdevice that is adapted to contain a plasma in the reactor.